Lithium secondary battery has recently been developed as a nonaqueous electrolyte secondary battery which is small and light, has a high energy density, and is capable of repeated discharge and charge, with the development of electronic devices. Lately, it has also been desired to develop a nonaqueous electrolyte secondary battery capable of fast charge and high output discharge, which is suitable as a secondary battery for cars such as a hybrid car and an electric car, or as a secondary battery for electric current storage which is used for electricity equalization.
It is necessary to take out electric current efficiently in order to improve a fast charge performance and a high output discharge performance of a nonaqueous electrolyte secondary battery. For this aim, it is desirable to derive current collector tabs from multiple points of an electrode. These current collection tabs are electrically connected to external terminals equipped on a lid through a lead. The lid further has a safety valve for releasing the pressure.
In one aspect, for example, in a case where a nonaqueous electrolyte secondary battery is loaded in an electric car, when a vibration or impact is applied to the battery from the outside, vibration of an electrode in the battery may be transmitted to a lid through a current collection tab and a lead, whereby a safety valve may be broken. In particular, in a case of a large-sized nonaqueous electrolyte secondary battery for a car, the electrode is also large, which increases the influence of vibration. For this reason, the risk of damage to a safety valve becomes large due the transmission of vibration.
JP-A No. 2002-279962 discloses a positive electrode current collector plate 82 in which an accordion-pressed plate 84 is linked to a fitting hole 91 for fitting a positive electrode terminal through a narrow section 92. The accordion-pressed plate 84 has folded parts 85A, 85B and 85C, and several laminated positive electrodes 87 are inserted into each folded parts. The narrow section 92 forms a current collecting path (see FIG. 13). In the positive electrode current collector 82 in JP-A No. 2002-279962, however, the transmission of vibration of the electrode to a positive electrode terminal cannot be inhibited, because the plate 84 and the fitting hole 91 are located on almost the same plane surface.
JP-A No. 2003-346771 discloses a current collecting connector 2 comprising a body 2a having an almost trapezoidal form and placed horizontally at ends of two power generation elements lined up. The current collecting connector 2 further comprises four electrode connecting parts 2b having long and narrow form and protruding downward from the body 2a. However, a large space is necessary for setting of the current collecting connector 2 in JP-A No. 2003-346771, because the electrode connecting parts 2b reach the lower end of an electrode from the body, and an energy density of a battery is reduced.
In another aspect, a problem occurs in which a welding yield is lowered depending on the method used for fixing a lid to a container. For example, if positions at which lid is fixed are not constant, not only battery sizes but also heights of electrode terminals attached to the lids vary. If the height of the electrode terminal is different from others in the single batteries, welding defects easily occur when an assembled battery is produced by welding the electrode terminals of the single batteries to electrically connect them. As a result, a welding yield is reduced. In addition, when an electrode terminal is fixed to a lid by caulking, the lid may be deformed by the caulking. When the lid is deformed, the degree of fitting between the lid and a case is degraded, and a gap is easily generated between the lid and the case. As a result, a welding yield is reduced in a welded part between the lid and the case.
A method for producing an angular sealed battery of JP-A No. 9-7557 is generally used for an alkali secondary battery such as a nickel-hydrogen secondary battery. According to JP-A No. 9-7557, when a fitted part between an opening end of a container and a lid plate is laser welded to seal the fitted part, a lid plate having a taper peripheral edge is used.
In a sealed battery in JP-A No. 10-144268, an inner peripheral edge of an opening part of a container is formed as a hole side taper, which is opened out, to receive a lid, and an outer periphery of the lid is formed as an axis side taper to fit in the taper of the opening part. Both tapers are formed so that the welding for joining the lid and the container can be performed from a direction toward a top surface of the lid, when the lid is fitted in the opening part of the container. According to JP-A No. 10-144268, the joined part between the lid and the container is welded from a direction toward the top surface of the lid in the state in which the lid is fitted in the opening part of the container.
In JP-A No. 9-7557 and JP-A No. 10-144268, the lids have the taper peripheral edge and do not have flanges. If an electrode terminal is fixed by caulking to the lid having such a shape, a position of the lid in the container easily varies when the lid is deformed by the caulking.
JP-A No. 2000-156219 illustrates, in FIG. 2, a sealed battery using a lid body with a flange. In the battery according to JP-A No. 2000-156219, the electrode terminal is hermetically sealed to the lid body via an insulating material. Thus, the problem of deformation of the lid body caused by the caulking does not occur in the battery according to JP-A No. 2000-156219.